It has long been appreciated that differential air pressure or “suction” may be utilized to retain or “suspend” a prosthetic limb on an amputee's stump. Gravitational and other forces tend to cause separation between the prosthetic limb and the patient's residual extremity during use. This happens, for example, during the swing phase of gait, when a prosthetic leg is additionally subjected to centrifugal forces. Patients have worn a variety of belts, straps, cuffs and harnesses to retain prosthetic limbs against separation from the residual limb. Such devices are inconvenient and can cause chafing against the patient's body giving rise to sores and abrasions.
The manner in which an artificial limb is suspended or attached to the residual limb determines the amount of control an amputee has over the prosthesis. Suction suspension typically involves the utilization of a socket liner and a “hard” stump socket. The liner, which is usually fabricated from silicone, fits snugly over the residual limb and is enveloped by the socket. A negative pressure between the liner-sheathed stump and the interior of the socket holds the prosthesis on the limb. The suspension method is advantageous since it gives the amputee the ability to better control the prosthesis and provides for useful sensory or proprioceptive feedback. Suction suspension also makes the prosthesis feel lighter, compared to other forms of suspension.
A valve is employed to regulate the air pressure in the socket such that undesirable pressure differentials do not prevent or complicate the donning and doffing of the socket. The valve also maintains suction once the socket has been satisfactorily clad. During donning, the patient's liner-sheathed stump is inserted into the socket. At some stage or stages during the insertion the socket liner will form a roughly circumferential air-tight seal through contact with the hard socket. As the patient's stump is inserted further into the socket, air pressure increases under the stump. A valve permits air to escape from the socket until the pressure inside the socket equalizes with the ambient pressure and, hence, allows the stump to be fully inserted inside the socket. As a result, when the stump is completely inserted in the socket, the air pressure is equal inside and outside the socket. The valve is closed allowing no air to flow into the distal end of the stump socket. Any tendency to remove the stump from the socket creates a “suction” effect that acts to maintain the socket on the stump. In this manner, the prosthesis is held on the patient's stump. During doffing of the stump from the socket the valve is opened to equalize the ambient pressure and the pressure inside the socket, thus dissipating the “suction” effect and allowing removal of the stump.
Though the principle of employing “suction” for “suspending” an artificial limb is clear, there are practical problems. One of these is the difficulty in providing a reliable and permanently effective seal at the proximal open end of the socket, this issue is important in maintaining the reduced pressure inside the socket. In some instances it is doubtful whether the suspending suctional force can independently support the weight of the lower limb prosthesis. This is problematic from a safety stand-point, because if the suspension fails, and there is no redundant or back-up support mechanism, the artificial limb could detach from the patient's stump.
U.S. Pat. No. 5,376,131 to Lenze, et al. discloses a socket with an elastic diaphragm that engages a patient's stump, and attempts to provide an effective seal, but the local constriction due to such a tight fitting diaphragm can result in impairment of circulation in the amputee's residual limb. Suspension sleeves, which are substantially elongated bands fabricated from a resilient material and envelop part of the stump and part of the outer socket, have been used to provide complementary mechanical support and may additionally function as a sealing means. Since these sleeves constrictingly grip the residual limb over a wide region they can limit limb movement or be uncomfortable.
Another approach has led to design of a socket liner which is attachable at its distal end to a socket or artificial limb. In this manner, the liner is mechanically secured and can provide additional suspension, if needed, or can play the role of a backup suspension means. Typically, the socket liner is equipped with a detachable attachment component, at its distal end, which mates with a locking device and hence secures the residual limb to an artificial limb. The locking devices employ a spring-loaded clutch mechanism or a pin-lock mechanism to lock to the liner attachment component. This attachment component is either a barb-shaped structure or a frictionally-retained pin. These attachment components can lock in a number of positions which affects the overall length of the prosthesis. Though this may be advantageous, it can make it difficult for the patient to consistently achieve the same prosthetic configuration when the residual limb and the artificial limb are articulated. Further, in this mode of limb suspension, the locking means and the valve means are autonomous entities which are separately invasive and additive in weight on the distal end of the socket.
Another type of suspension device is a roll-on suction socket. The suction socket, which is typically fabricated from silicone, is a long tubular structure with one open end. The distal end of the suction socket is attachable to a prosthesis via an attachment component and a locking device employing the same principle and design described above. During donning, the suction socket is turned inside out and rolled on to the residual stump, being careful to avoid trapping air between the skin of the limb and the suction socket. Since the suction socket creates/destroys a partial vacuum at its distal end during rolling-on/rolling-off of the socket the function of a valve is intrinsically incorporated into the donning/doffing technique. Thus, the suction socket is a simple and effective device to suspend a prosthesis. But, this can be misleading because the suction socket may not be sealingly gripped by the hard socket, thereby converting the suction socket to a “traction” socket. Thus, the prosthesis is suspended onto the residual limb by a combination of the frictional adhesive traction of the suction socket and the locking retention due to the locking device. This skin traction causes an undesirable “tethering” effect by pulling on the skin, thereby creating multiple skin problems. The length of the tube can also interfere with the mobility of the residual limb, especially in the case of below-knee amputees.
Once a desired suspension device has been assimilated into the prosthesis, the prosthesis must be laterally aligned with respect to the residual limb. A typical conventional method for alignment of a prosthesis involves the use of a multi-axis slide mechanism which adjusts with two degrees of freedom. The alignment is reached by adjusting the relative horizontal positioning between two plates, one of which is attached to the distal end of the socket and the other to the top end of the artificial limb. Each plate has a centrally located slot and the slots are perpendicularly oriented to one another. Once the proper alignment has been ascertained a fastening means, such as a nut/bolt/washer combination couples the residual limb with the artificial limb. Such an alignment mechanism can be hazardous. During use of the prosthesis the interface between the socket and the artificial limb is subjected to stresses and moments that can result in relative motion between the alignment plates, thus misaligning the prosthesis. In extreme cases, the coupling plates may become unfastened, thereby, placing the patient at risk. The conventional alignment device adds excess weight to the prosthesis as well as adding to the cost, since it is a complicated device which is fabricated from titanium. Also, the size of the alignment device undesirably adds to the overall length of the prosthesis, which can be problematic when accommodating long stump lengths.
Despite the large number of suspension options available, none act to eliminate rotation between the hard socket and the suction liner. A design called a “quad socket” has been also used. The quad socket is shaped in a square manner and forcing the “cylindrical” limb into this square receptacle makes the prosthesis less apt to rotate on the limb. This is not comfortable for the limb. Therefore, there has been a trend toward more naturally-shaped sockets, making rotation control even more difficult.
There is a need for an improved attachment system for prosthetics. Also, there is a need for improving retention of the stump in the socket without sacrificing the patient's comfort and without compromising expense, weight, or simplicity of use. There also is a need for improving rotation control, which will improve the patient's overall comfort and agility.